Resnick was a pioneer in the field of recommender systems (sometimes called collaborative filtering). Recommender systems guide people to interesting materials based on recommendations from other people. The GroupLens system he helped develop was awarded the 2010 ACM Software Systems Award.
He has developed longitudinal metrics tracking social media behavior, including the Iffy Quotient and the H|O|T Speech Metric. Most recently, he developed the Community Notes Monitor, providing data about the scope and speed of X’s Community Notes and a tutorial that explains the technical details of their bridging vote counting algorithm through the actual votes on any community note.
He also has developed, with Grant Schoenebeck and others, the Rater Equivalence technique for expressing the performance of an automated classifier when only noisy human labels are available and the alternative to using the automated classifier is to use panels of human raters.
He also developed, with Jessica Hullman and Eytan Adar, Hypothetical Outcome Plots, a way to use animation to provide a better visual representation of uncertainty than is provided by conventional error bars.